Composite material, composite carbon material and method for producing those

ABSTRACT

The present invention provides a composite material and a carbonized composite material having high electric conductivities and heat conductivities, in each of which nanocarbons are uniformly mixed, and a method for producing the materials. The composite material of the present invention comprises: a high polymer, in which an atomic group including a heteroatom, such as nitrogen, oxygen or sulfur, exists in a main chain or a side chain; and nonocarbons. The carbonized composite material of the present invention is produced by burning the above described composite material.

FIELD OF TECHNOLOGY

The present invention relates to a composite material, a carbonizedcomposite material and a method for producing the materials.

BACKGROUND TECHNOLOGY

Conventionally, electrically conductive paste, electrically conductiveink, electrically conductive film and heat conductive film are producedby mixing a substance having high electric conductivity, e.g., carbonblack, silver, or a compound thereof with resin, an organic solvent orthe like.

Patent Document 1: Japanese Patent Kokai-Gazette No. 2005-62835

Patent Document 2: Japanese Patent Kokai-Gazette No. 2005-54094

Patent Document 3: Japanese Patent Kokai-Gazette No. 2005-54095.

Patent Document 4: Japanese Patent Kohyo-Gazette No. 2002-544346.

Patent Document 5: Japanese Patent Kokai-Gazette No. 2000-63726.

DISCLOSURE OF THE INVENTION

When an electric current passes through the substance having highelectric conductivity or the substance is oxidized, the substance issulfurated so that electric conductivity, heat conductivity andelectromagnetic shielding performance get unstable, further a weight ofthe substance is heavy so that uses of the substance are limited. Incase of using a metal as the conductive substance, it has poorflexibility. On the other hand, in case of using carbon black as theconductive substance, it has enough flexibility but has low electricconductivity, low heat conductivity and poor electromagnetic shieldingperformance.

The present invention was conceived to solve the above describedproblems, and an object of the present invention is to provide acomposite material and a carbonized composite material having goodelectric conductivities, heat conductivities and electromagneticshielding performance, in each of which nanocarbons are uniformly mixed,and a method for producing the materials.

The composite material of the present invention comprises: a substancederived from a high polymer having a molar weight of 50-1,000,000, inwhich an atomic group including a heteroatom, such as nitrogen, oxygenor sulfur, exists in a main chain or a side chain; and nanocarbons.

The composite material of the present invention is produced bydispersing nanocarbons in a solution of a high polymer substance havinga molar weight of 50-1,000,000, in which an atomic group including aheteroatom, such as nitrogen, oxygen or sulfur, exists in a main chainor a side chain, and drying the solution, so that the nanocarbons areincorporate in the high polymer substance.

The composite material is characterized by being formed into a film- orsheet-shape.

The composite material is characterized by being formed into agrain-shape.

The composite material is characterized in that a weight of nanocarbonswith respect to that of the high polymer substance is 1-30 wt %.

The composite material is characterized in that the high polymersubstance contains amino acid, protein made from amino acid or peptide.

The composite material is characterized in that the high polymersubstance is made from a silk material.

The carbonized composite material of the present invention is producedby burning the above described composite material.

The carbonized composite material is characterized by being burned attemperature of 500-3000° C.

The method for producing the composite material comprises the steps of:dispersing nanocarbons in a solution of a high polymer substance havinga molar weight of 50-5,000,000, in which an atomic group including aheteroatom, such as nitrogen, oxygen or sulfur, exists in a main chainor a side chain; and drying the solution, in which the nanocarbons aredispersed.

The method further comprises the step of applying a magnetic field tothe solution, in which the nanocarbons are dispersed, so as to orientatethe nanocarbons.

The method is characterized in that a weight of nanocarbons with respectto that of the high polymer substance is 1-30 wt %.

The method is characterized in that the high polymer substance containsamino acid, protein made from amino acid or peptide.

The method is characterized in that the high polymer substance is a silkmaterial.

The method for producing the carbonized composite material comprises thesteps of: dispersing nanocarbons in a solution of a high polymersubstance, in which an atomic group including a heteroatom, such asnitrogen, oxygen or sulfur, exists in a main chain or a side chain;drying the solution, in which the nanocarbons are dispersed; and burningthe dried substance.

The method is characterized in that the burning step includes thesub-steps of: primary-burning at low temperature; and secondary-burningat high temperature.

The method is characterized in that a weight of nanocarbons with respectto that of the high polymer substance is 1-30 wt %.

The method is characterized in that the high polymer substance containsamino acid, protein made from amino acid or peptide.

The method is characterized in that the high polymer substance is a silkmaterial.

EFFECTS OF THE INVENTION

In the present invention, the nanocarbons can be uniformly mixed, sothat the composite material and the carbonized composite material havinggood electric conductivities, heat conductivities and electromagneticshielding performance can be provided.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is an explanation view of a composite material.

FIG. 2 is a raman spectrum chart of a burned body, which was formed byburning a coarse-grained silk at temperature of 2,000° C.

FIG. 3 is a raman spectrum chart of a burned body, which was formed byburning a coarse-grained silk at temperature of 700° C.

FIG. 4 is a raman spectrum chart of a burned body, which was formed byburning a coarse-grained silk at temperature of 1,000° C.

FIG. 5 is a raman spectrum chart of a burned body, which was formed byburning a coarse-grained silk at temperature of 1,400° C.

FIG. 6 is a SEM photograph of a composite material of Example 1.

FIG. 7 is a SEM photograph of the composite material of Example 1.

FIG. 8 is a SEM photograph of the composite material of Example 1.

FIG. 9 is a SEM photograph of a composite material of Example 2.

FIG. 10 is a SEM photograph of the composite material of Example 2.

FIG. 11 is a SEM photograph of the composite material of Example 2.

FIG. 12 is a SEM photograph of the composite material of Example 2.

FIG. 13 is a SEM photograph of a carbonized composite material formed byburning the composite material of Example 2.

FIG. 14 is a SEM photograph of the carbonized composite material formedby burning the composite material of Example 2.

FIG. 15 is a SEM photograph of the carbonized composite material formedby burning the composite material of Example 2.

FIG. 16 is a SEM photograph of the carbonized composite material formedby burning the composite material of Example 2.

FIG. 17 is a SEM photograph of a composite material of Example 4.

FIG. 18 is a SEM photograph of the composite material of Example 4.

FIG. 19 is a SEM photograph of the composite material of Example 4.

FIG. 20 is a SEM photograph of the composite material of Example 4.

FIG. 21 is a SEM photograph of a composite material of Example 5.

PREFERRED EMBODIMENTS OF THE INVENTION

FIG. 1 is an explanation view of a sheet-shaped (including a film-shape)composite material 10, in which nanocarbons 14 are mixed with a highpolymer substance 12, in which an atomic group including a heteroatom,such as nitrogen, oxygen or sulfur, exists in a main chain or a sidechain.

Note that, a nanocarbon is a nanosize carbon such as single-layered,two-layered or multilayered carbon nanotube, cap stack-type carbonnanotube, carbon nanohorn or fullerene.

For example, the sheet-shaped composite material 10 is produced by thesteps of: dispersing nanocarbons in a solution (a high polymer solution)derived from the above described high polymer substance having a molarweight of 50-5,000,000; spreading the solution, in which the nanocarbonsare dispersed, on a proper substrate; and drying the solution at theroom temperature or high temperature so as to form into the sheet-shape.To disperse the nanocarbons in the high polymer solution, supersonicwaves may be applied to the solution in which the nonocarbons are added.

By applying a magnetic field to the solution, the fiber-shapednanocarbons, e.g., carbon nanotubes, can be oriented in a prescribeddirection. By drying the solution, the composite material 10, in whichmost of the nanocarbons are oriented in the prescribed direction, can beobtained.

The composite material 10 may be formed by dispersing nanocarbons in thehigh polymer solution and drying the solution including the nanocarbons,and it may be formed into a sheet-shape or a grain-shape; further, asheet-shaped carbonized composite material can be obtained by burningthe sheet-shaped composite material 10 at temperature of about500-3,000° C. Electric conductivity of the high polymer can be increasedby the burning process, and the nanocarbons originally have goodelectric conductivity, so the sheet-shaped carbonized composite materialhaving good electric conductivity can be produced. By dispersingnanocarbons in the high polymer solution, drying the solution andburning the dried substance, the carbonized composite material havinguniform electric conductivity, in which the nanocarbons are uniformlymixed, can be obtained.

The sheet-shaped carbonized composite material, which is produced byburning the composite material 10 in which the nanocarbons have beenoriented in the prescribed direction by applying a magnetic field, hasgood heat conductivity too.

A fiber-shaped nanocarbon, e.g., a carbon nanotube, has heat conductiveanisotropy, especially has excellent heat conductivity in an axialdirection, but has low heat conductivity in radial directions. Byorienting nanocarbons in the prescribed direction and burning, thecarbonized composite material having excellent heat conductivity in theorienting direction of the nanocarbons can be produced.

In the above described embodiment, the composite material 10 is formedinto the sheet-shape, further the high polymer solution, in whichnanocarbons are dispersed, may be merely dried. The dried substance isformed into grains or a block, and the grain- or block-shaped driedsubstance is burned at temperature of 500-3,000° C., then the burned orcarbonized substance is crushed to form into grain-shaped carbonizedcomposite materials having desired sizes. Of course, the sheet-shapedcarbonized composite material may be crushed to form into grains.

The grain-shaped carbonized composite material also has good electricconductivity. Therefore, it may be suitably used as a material ofelectrically conductive paste and electrically conductive ink. Anelectromagnetic shielding member can be produced by applying theelectrically conductive paste or electrically conductive ink to asubstrate or incorporating the same into the substrate.

By mixing the composite material with resin or metals, various materialshaving good electric conductivities and heat conductivities can beproduced.

Note that, a proper weight of nanocarbons with respect to that of thehigh polymer substance is about 1-30 wt %, more preferably 5-10 wt %.

Silk materials may be used as the high polymer substance.

The silk materials include woven fabrics, knitted works, powders, cloth,strings, etc. made of threads of domesticated or wild silk worms. Theymay be used as single or in combination.

The silk materials have higher-order structures of protein, and variouscoordinating groups including amino acid residues exist in theirsurfaces (including inner faces of foldable structures).

Besides the above described silk materials, high polymers, in each ofwhich an atomic group including a donor atom, such as nitrogen, oxygenor sulfur, exists in a main chain or a side chain, may be used as thehigh polymer substances.

For example, keratin, milk protein, corn protein, collagen, etc. may beused as the high polymer substances.

In the following description, the silk material is used as the highpolymer substance.

The silk materials were burned, and solid state properties of the burnedbodies were examined.

The silk materials were burned at temperature of about 500-3,000° C.

A burning atmosphere was an inert gas atmosphere, e.g., nitrogen gasatmosphere, argon gas atmosphere, or a vacuum atmosphere so as not toburn the silk materials to cinders.

The silk materials should be burned in stages without rapid burning.Further, the above described composite material should be burned by thesame manner.

For example, each silk material was primary-burned in the inert gasatmosphere with low temperature rising rate of 100° C./hour or less,preferably 50° C./hour or less, until reaching a first temperature(e.g., 500° C.), then the first temperature was maintained for severalhours. The silk material was once cooled until reaching the roomtemperature, then the silk material was secondary-burned in the sameatmosphere with low temperature rising rate of 100° C./hour or less,preferably 50° C./hour or less, until reaching a second temperature(e.g., 700° C.) and the second temperature was maintained for severalhours. Then, the silk material is cooled. Further, the silk material wastertiary-burned at final burning temperature (e.g., 2000° C.) by thesame manner so as to obtain a burned or carbonized object. Note that,the burning conditions are not limited to the above described examples,and they may be optionally changed on the basis of kinds of silkmaterials, functions of carbonized materials, etc.

By burning the silk material in stages and burning with the lowtemperature rising rate, rapid decomposition of the protein high-orderstructure, in which crystalline forms and noncrystalline forms of adozen of amino acids are combined, could be avoided.

FIG. 2 is a raman spectrum chart of a burned body, which was produced byburning a coarse-grained silk at temperature of 2,000° C. (the finalburning temperature). Peaks were observed at 2681 cm⁻¹, 1570 cm⁻¹ and1335 cm⁻¹, so the coarse-grained silk was graphitized.

FIGS. 3-5 are raman spectrum charts of burned bodies, which wereproduced by respectively burning coarse-grained silks at 700° C., 1,000°C. and 1,400° C. By burning at 1,400° C., peaks were low but observed atthe same three points.

By burning at 1,000° C. or below, no peaks were observed, so the burnedbodies were not graphitized and they do not have high electricconductivities.

Therefore, the silk materials, which will be used as electricallyconductive materials, should be burned at high temperature, e.g.,1,000-3,000° C. (the final burning temperature).

Specific resistances of the burned silk materials (woven cloth) burnedat 1,400° C. and 2,000° C. were measured, the results of the bothsamples (filaments of single yarns) were about 1×10⁻⁵ (Ω·m), which wasgreater than that of graphite (4-7×10⁻⁷ Ω·m) but smaller than that ofcarbon (4×10⁻⁵), so they had good electric conductivities.

Therefore, it is clear that the carbonized composite material of thepresent invention, which is a composite material constituted by theburned silk material and nanocarbons, has good electric conductivity.TABLE 1 Elements C N O Na Mg Al Si P S Cl K Ca Fe Wt % 66.1 27.4 2.1 0.10.3 0.1 0.3 0.1 0.1 0.1 0.1 3.2 0.2

Table 1 shows results of elemental analysis (semiquantative analysis) ofa burned product, which was a knitted work made of silk of domesticatedsilkworms and which was burned in a nitrogen atmosphere at 700° C.,performed by an electron beam micro analyzer.

Measuring conditions were as follows: accelerating voltage was 15 kV;irradiating current was 1 μA; and probe diameter was 100 μm. Note that,values in the table indicate tendency of detected elements but they arenot guaranteed values.

According to Table 1, a large amount of nitrogen, i.e., 27.4 wt %, wasremained. Further, other elements derived from amino acids were alsoremained.

By primary-burning the silk material at relatively low temperature, alarge amount of elements, e.g., nitrogen elements, were remained. Thenitrogen elements remained were derived from amino acid residues.

If the nitrogen elements are remained, the composite resin material canbe suitably mixed with high dispersibility and adhesiveness.

EXAMPLE 1

A silk material of 240 g was added to a solution 11, which includes 65%of calcium chloride dihydrate, and dissolved therein for six hours attemperature of 95° C. After completing the dissolution, a silk proteinsolution was obtained by the steps of: filtering the solution to removenon-dissolved substances; demineralizing the filtered solution by adialyzing membrane, whose molecular fraction was 300; and diluting thesolution until reaching concentration of 3%. Carbon nanotubes of 1 gwere mixed with the silk protein solution of 3 ml, then supersonic waveswere applied to the mixed solution for 30 minutes so as to disperse thecarbon nanotubes therein.

The solution including the carbon nanotubes was applied on a plate(acrylic plate) and dried at the room temperature so as to obtain acomposite material.

SEM photographs of the composite material are shown in FIGS. 6-8. Notethat, magnifications are indicated as “1K”, etc. For example, “1K” means1×10³. As clearly shown in FIG. 8, the carbon nanotubes were uniformlydispersed in the composite material.

EXAMPLE 2

A silk material of 240 g was added to the solution 11, which includes65% of calcium chloride dihydrate, and dissolved therein for six hoursat temperature of 95° C. After completing the dissolution, a silkprotein solution was obtained by the steps of: filtering the solution toremove non-dissolved substances; demineralizing the filtered solution bya dialyzing membrane, whose molecular fraction was 300; and diluting thesolution until reaching concentration of 3%. Then, a gel includingcarbon nanotubes (CNTs) was formed by the steps of: mixing CNTs of 1 gwith the silk protein solution of 3 ml; applying supersonic waves to themixed solution for 30 minutes so as to disperse the CNTs therein;heating the mixed solution; and recrystallizing silk.

The gel was dried by hot air of 80° C. and formed into dry powders.

SEM photographs of the dry powders are shown in FIGS. 9-12. As clearlyshown in the photographs, the carbon nanotubes were uniformly dispersedin particles.

EXAMPLE 3

A carbonized composite material was produced by burning the powders ofExample 2, in an inert gas atmosphere, at temperature of 700° C. SEMphotographs of the carbonized composite material are shown in FIGS.13-16.

The carbonized composite material and epoxy resin, whose weight ratiowas 2:1, were mixed to produce a composite resin material. Heatconductivity of the composite resin material was measured, by laserflash method, at the room temperature, and the result was 11 W/m·k.

Note that, a carbonized material, which was produced by burning a silkmaterial (a coarse-grained silk) at temperature of 700° C., and epoxyresin, whose weight ratio was 2:1, were mixed to produce a compositeresin material, then heat conductivity of the composite resin materialwas measured, by laser flash method, at the room temperature, and theresult was 0.2 W/m·k.

The heat conductivity of the carbonized composite material of Example 3was higher than that of the composite material formed by mixing the merecarbonized silk material with the resin.

The heat conductivity of the carbonized composite material can befurther increased by selecting kinds of nanocarbons, mixture ratio ofnanocarbons and a carbonized silk material, kinds of resin, burningtemperature, etc.

EXAMPLE 4

A silk material of 240 g was added to the solution 11, which includes65% of calcium chloride dihydrate, and dissolved therein for six hoursat temperature of 95° C. After completing the dissolution, a silkpeptide solution was obtained by the steps of: adding protease of 1 g tothe solution; maintaining temperature of the solution at 50° C. for 20hour; filtering the solution to remove non-dissolved substances;demineralizing the filtered solution by a dialyzing membrane, whosemolecular fraction was 300; and diluting the solution until reachingconcentration of 10%. Then, carbon nanotubes of 1 g was mixed with thesilk peptide solution of 5 ml, then supersonic waves were applied to themixed solution for 30 minutes so as to disperse the CNTs therein.

A magnetic field of four tesla was applied to the solution, then thesolution was applied on a plate (acrylic plate) and dried at the roomtemperature so as to obtain a sheet-shaped composite material. SEMphotographs of the composite material are shown in FIGS. 17-20. Asclearly shown in the photographs, most of the CNTs were oriented in acertain direction.

EXAMPLE 5

Two-layered carbon nanotubes of 1 g was mixed with 5 ml of the silkpeptide solution of Example 4, then supersonic waves were applied to themixed solution for 30 minutes so as to disperse the CNTs therein.Grain-shaped carbonized composite materials were produced by the stepsof: applying the solution on a plate; drying the solution by hot air of60° C.; primary-burning in an inert gas atmosphere at temperature of700° C.; secondary-burning at temperature of 1,400° C.; and crushing thecarbonized substance. An SEM photograph of the grain-shaped carbonizedcomposite material is shown in FIG. 21.

EXAMPLE 6

Powder resistance of a carbonized composite material was measured underthe following conditions.

A cylindrical member having an inner diameter of 4.5 cm, which was madeof an insulating material, was filled with the composite powders ofExample 5, a pressure of 500 kg/cm² was applied to the composite powdersfrom the upper side until thickness of the composite powders reached 2mm, and an electric current of 10 mA was applied to the compositepowders with maintaining that pressure; the resistance was 18.02×10⁻⁵Ω·m.

COMPARATIVE EXAMPLE 1

A cylindrical member having an inner diameter of 4.5 cm, which was madeof an insulating material, was filled with copper electrolytic powders(particle diameters 2-3 μm), a pressure of 500 kg/cm² was applied to thepowders from the upper side until thickness of the powders reached 2 mm,and an electric current of 1 A was applied to the powders withmaintaining that pressure; the resistance was 19.29×10⁻⁵ Ω·m. Note that,in case of copper, an oxide film was formed by applying an electriccurrent of 10 mA, thus the resistance was measured with such highcurrent value so as not to badly influence the resistance.

COMPARATIVE EXAMPLE 2

A cylindrical member having an inner diameter of 4.5 cm, which was madeof an insulating material, was filled with graphite, a pressure of 500kg/cm² was applied to the graphite from the upper side until thicknessof the graphite reached 2 mm, and an electric current of 10 mA wasapplied to the graphite with maintaining that pressure; the resistancewas 44.82×10⁻⁵ Ω·m. Note that, in case of copper, an oxide film wasformed by applying an electric current of 10 mA, thus the resistance wasmeasured with such high current value so as not to badly influence theresistance.

As described above, the composite powders of the example had lowresistance and high electric conductivity. Since the composite powdershad high electric conductivity, it had high electromagnetic shieldingperformance.

The electric conductivity of the carbonized composite material can befurther increased by selecting kinds of nanocarbons, mixture ratio ofnanocarbons and a carbonized silk material, kinds of resin, burningtemperature, etc.

1. A composite material comprising: a substance derived from a highpolymer having a molar weight of 50-1,000,000, in which an atomic groupincluding a heteroatom, such as nitrogen, oxygen or sulfur, exists in amain chain or a side chain; and nonocarbons.
 2. A composite materialproduced by dispersing nanocarbons in a solution of a high polymersubstance having a molar weight of 50-1,000,000, in which an atomicgroup including a heteroatom, such as nitrogen, oxygen or sulfur, existsin a main chain or a side chain, and drying the solution, whereby thenanocarbons are incorporate in the high polymer substance.
 3. Thecomposite material according to claim 2, wherein the composite materialis formed into a film- or sheet-shape.
 4. The composite materialaccording to claim 2, wherein the composite material is formed into agrain-shape.
 5. The composite material according to claim 2, wherein aweight of nanocarbons with respect to that of the high polymer substanceis 1-30 wt %.
 6. The composite material according to claim 2, whereinthe high polymer substance contains amino acid, protein made from aminoacid or peptide.
 7. The composite material according to claim 2, whereinthe high polymer substance is made from a silk material.
 8. A carbonizedcomposite material produced by burning the composite material accordingto claim
 2. 9. The carbonized composite material according to claim 8,wherein the composite material is burned at temperature of 500-3000° C.10. A method for producing a composite material, comprising the stepsof: dispersing nanocarbons in a solution of a high polymer substancehaving a molar weight of 50-5,000,000, in which an atomic groupincluding a heteroatom, such as nitrogen, oxygen or sulfur, exists in amain chain or a side chain; and drying the solution, in which thenanocarbons are dispersed.
 11. The method according to claim 10, furthercomprising the step of applying a magnetic field to the solution, inwhich the nanocarbons are dispersed, so as to orientate the nanocarbons.12. The method according to claim 10, wherein a weight of nanocarbonswith respect to that of the high polymer substance is 1-30 wt %.
 13. Themethod according to claim 10, wherein the high polymer substancecontains amino acid, protein made from amino acid or peptide.
 14. Themethod according to claim 10, wherein the high polymer substance is asilk material.
 15. A method for producing a carbonized compositematerial, comprising the steps of: dispersing nanocarbons in a solutionof a high polymer substance, in which an atomic group including aheteroatom, such as nitrogen, oxygen or sulfur, exists in a main chainor a side chain; drying the solution, in which the nanocarbons aredispersed; and burning the dried substance.
 16. The method according toclaim 15, wherein the burning step includes the sub-steps of:primary-burning at low temperature; and secondary-burning at hightemperature.
 17. The method according to claim 15, wherein a weight ofnanocarbons with respect so that of the high polymer substance is 1-30wt %.
 18. The method according to claim 15, wherein the high polymersubstance contains amino acid, protein made from amino acid or peptide.19. The method according to claim 15, wherein the high polymer substanceis a silk material.